A common communication application is a pair of transceivers engaged in bidirectional communication. A recently popular application is in radio telephony or cellular radio. It is particularly efficient, both from the radio spectrum standpoint as well as equipping the transceivers, if the transceivers can operate on a common carrier frequency. Typically, however, the users are accustomed to full-duplex operation, where at least the appearance of "talking" and "hearing" simultaneously are supported. The radio carrier link between the transceivers is, however, a half-duplex link, i.e. at any instant of time, it can only carry a signal from one transceiver to the other. The perception of full-duplex operation can be achieved, however, by framing the communication and allocating half of each frame to transmissions of one of the two transceivers. In this fashion, each transceiver has an opportunity to transmit during the frame and by buffering the signals, the appearance of full duplex operation is supported.
In a system of the foregoing type, the design must take into account the fact that the system clocks in each of the two transceivers will necessarily differ, however slightly, in frequency, since no two independent time bases can be made to oscillate at exactly the same frequency. Even the smallest frequency discrepancy will eventually result in buffer overflow or underflow with consequent disruption of the communications. The present invention is directed at a method and apparatus for attaining coarse frequency lock between the synchronous data clocks in both of the transceivers, thereby avoiding buffer underflow or overflow.